Notice that these images were scanned in with the intent that they would only be viewed on a monitor. Thus, the images included here are only 72dpi and are stored as gif images (only 8-bit color).
Most of these images are Copyright Steve Finberg. If you would like photographic prints or slides of any of these images, please send email to Steve Finberg at w1gsl@athena.mit.edu
The Team
1989 (MIT Crew Boathouse, Charles River, Boston)
1992 (Los Angeles, California)
In December of 1992 the team flew to Los Angeles to race Decavitator (with its newly fabricated fairing) in what would be its last race - an IHPVA event.
Fabrication
Glass molds were used for first composite parts. To make the molds, a male master was cut from foam then glassed. After hours of sanding and polishing the foam/glass plug was sprayed with mold release then used as a mandrel for the female mold.
Aluminum molds were later used to build composite parts. Instead of laying up a female mold on a male plug, the cavities were machined directly from large chunks of aluminum. After minor sanding and polishing, the parts could then be cast directly in the molds. Instead of the 6 weeks required to go from design to finished part using composite molds, the direct machining took only 6 days.
The aluminum molds were machined on a 3-axis NC milling machine. The milling machine was a rather primitive Cincinati Milicron with very limited memory and interfacing abilities.
Hulls were built at Composite Engineering and assembled at MIT. The hulls began life as full-sized women's kayaks. The top 3 inches or so were chopped off, then plywood bulkheads and a deck were added to form a watertight shell.
The canards went through a marked reduction in size over 3 years. The inverted T on the left is from the most recent, world-record-setting configuration. The inverted T on the right is the tail from the original V-foil configuration.
The wings also went through a reduction in size (that's an old punch card in the middle for scale). The original 'V' foil is in the back. The wing from the world-record-setting run is in the front.
Marc Schafer putzes with his timing system. The system uses a bright light on one side of the river and a photo sensor in a tube on the other size of the river. Anything that crosses the line between the light and the sensor will trigger the sensor.
Flight
The V-foil did fly, but not very well. Here Mark pitches up just before ventilating (and subsequently crashing down).
A full-sized fairing was built to completely enclose the pilot. The fairing reduced drag, but introduced instability. As a result, the boat was very unstable at high speeds and nearly uncontrollable.
Tips for Do-It-Yourself Hydrofoilers
This is what happens when the wing is too big. When close to the surface, the large wing caused more drag than lift because of the surface effects. Here you can see water pouring over the wing as if it were a dam.
Stiffness of the superstructure is of primary importance. Early versions of Decavitator used only thin wires to hold the hulls in position relative to the fuselage. A tetrahedron made of carbon tubes was later built to eliminate the twist you see here.
Roll stability was always an issue. At high speeds the foils can ventilate or stall, creating drag at one wing tip or the other. The mass of the pilot and boat want to continue in the direction they were heading, and the vehicle starts to roll over.
The drawbacks of V-foils at high speed are apparent here. If you look closely at the wing beneath the pilot you will see two white streaks where the V enters the water. The shallow angle of the V foil encouraged ventilation; air would get sucked down the top of the foil.
Miscellaneous
Dropping the chain on the river was a problem. The decavitator drive system was designed to be pedalled only forward; if you pedalled backward or suddenly stopped pedalling, the chain popped off the sprockets.
Helmet, just in case. The first day out we had no idea what to expect, and Mark was planning to go really fast.
Putting a 15x10x10 ft, 40 lb boat into the water isn't easy... It took four people to put the boat (gently) into the water, and two people to counterbalance the pilot as s/he slid out the cantilevered beam from the dock to the 'cockpit'.
And sqeezing a 6 foot tall, 140 pound pilot into the rather confined, very hot fairing was almost as difficult.
Mark Drela takes a water break between runs in California.
Have boat, will travel. Decavitator just barely fit into the back of this 24 foot rental truck.
The Competition
The Flying Fish II
The Hydroped
The Hydroped chases some ducks.
The competition came in all sorts...
...and sizes.
